Microsensors have been used with great success in a wide variety of applications over the years, particularly during the last decade. Market demand for chemical sensors in the United States alone is projected to surpass $5 billion by 2012. Glucose biosensors will likely be the largest type of chemical sensor, by volume, as the increasing number of diagnosed diabetics continues to boost demand for electronic blood glucose monitors.
Biomedical engineers were among the first to exploit the possibilities of microelectronic chip technology to develop silicon-based sensors. Their development of this technology provided clinicians with these sensors, which became cheaper over time. All the while, the performance of these sensors improved, following the trend in Moore's law for digital integrated circuits (ICs). This concept has developed over the years into a large family of about sixty different device types based on some form of field effect transistor (FET). For each application, the gate of the FET has been designed to make the device sensitive to either chemicals, ions, radiation, or even the voltage of individual strands of DNA. In these FETs, the normal gates are typically replaced with a sensitive metal or membrane that, in effect, acts as a collector of trapped charges/dipoles, i.e., an electric field (e-field) sensor. Due to limitations in threshold voltage gain and inefficiencies in removing trapped charges/dipoles after a sensing event, however, there are presently limitations in the sensitivity and selectivity of FET devices in these sensors.